1. Field of the Invention
The present invention relates to wireless communication technology. More particularly, the present invention relates to a method and apparatus for establishing a connection between evolved Node Bs (eNBs).
2. Description of the Related Art
With the development of the communication technologies, the mobile communication system has developed the System Architecture Evolution (SAE) system. The SAE system includes the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and core network. FIG. 1 is a schematic diagram illustrating the structure of an SAE system according to the related art.
Referring to FIG. 1, eNBs, which are responsible for providing wireless interfaces used for accessing the SAE system for mobile phones, belong to the wireless access network. The Mobility Management Entity (MME) and Service Gateway (S-GW) belong to the core network, and connect with an eNB through an S1 interface (the S1 interface link marked with the dotted line in FIG. 1). The MME is responsible for managing mobile contexts, session context of the User Equipment (UE) and saving information relating to the security of the user. The S-GW is mainly used for providing the user plane function. The MME and the S-GW may be located at a same physical entity. Each eNB connects with multiple MMEs in the MME pool. Each eNB connects with multiple S-GWs in the S-GW pool.
An interface between two eNBs is called an X2 interface (the X2 interface connection in FIG. 1 is marked with a solid line). When a user in a connection mode moves from a source eNB to a target eNB, if there is a direct X2 interface between the two eNBs, the source eNB initiates an X2 interface based handover process. Specifically, the source eNB sends a message to the target eNB for conveying necessary information. The necessary information refers to an X2 signaling context indication, a core network indication, an Identification (ID) of the target cell, encryption ability and encryption information of the UE, connection context information and data bearer Enhanced-Radio Access Bearer (E-RAB) information allocated by the source eNB for the UE. The target eNB prepares resources and notifies the UE of the new configuration of the target cell through the source eNB. The new configuration includes the X2 signaling context indication and a Radio Resource Control (RRC) message to be sent to the UE allocated by the target eNB for the UE. The RRC message to be sent to the UE is transparently transmitted to the source eNB. The source eNB sends the message to the UE. The UE is synchronized to the target cell, and sends the message to the target eNB. The target eNB receives the message of the UE, and sends the message to the MME, and switches a downlink data tunnel from the source cell to the target cell. If there is no X2 interface between two eNBs, the source eNB initiates an S1 interface based handover process, i.e. the source eNB sends a message to the MME of the core network. The MME forwards the message between the source eNB and the target eNB.
In the Long Term Evolution-Advanced (LTE-A) system, besides the eNBs, there are two other kinds of access equipment. The two kinds of access equipment connect with each other by accessing other network nodes and the core network, and forward data through the other network nodes, including a Relay eNB or Home eNB (HeNB), etc.
FIG. 2 is a schematic diagram illustrating network connections of a Relay eNB according to the related art.
Referring to FIG. 2, the eNB connecting with the Relay eNB is called the Dedicated eNB (DeNB). The Relay eNB connects with the DeNB. After startup, the Relay eNB establishes an RRC connection with the DeNB. The S1 and X2 interfaces are used for the RRC connection and the S1 and X2 interfaces of the Relay eNB end at the Relay. The DeNB provides an agent function of the S1 and X2 interfaces between the Relay eNB and other network nodes.
FIG. 3 is a flowchart illustrating a method for establishing the S1 and X2 interfaces after a Relay eNB starts up according to the related art. As shown in FIG. 3, the following steps are included.
Step 301: After startup, the Relay eNB first establishes a RRC connection between the DeNB.
Step 302: The Relay eNB performs UE attachment registration, for sending the information of the UE to the MME. The MME saves the information of the UE and allocates a temporary ID for the UE. The process has been defined.
Step 303: A default bearer and UE contexts are established between the MME and DeNB.
Step 304: The DeNB initiates an RRC reconfiguration for reconfiguring the established RRC.
Step 305: The Relay eNB sends an S1 establishment request message, including information such as a Tacking Area Code (TAC) supported by the Relay eNB and Public Land Mobile Network ID (PLMN Id) to the DeNB.
Step 306: The DeNB sends an S1 establishment response message to the Relay eNB. The S1 establishment response message includes the information of the MME providing services to the Relay eNB, such as the operator of the MME, a group code of the MME, an MME code and an MME name.
If the TAC supported by the Relay eNB is different from that supported by the DeNB, step 307 is performed; otherwise step 309 is performed.
Step 307: The DeNB sends an eNB configuration transmission message to the MME, for updating a TAC list supported by the DeNB.
Step 308: The MME sends an MME configuration transmission response message to the DeNB.
Step 309: The Relay eNB sends an X2 establishment request message to the DeNB. The X2 establishment request message includes information of cells of the Relay eNB. Optionally, the message includes information of neighboring cells of the Relay eNB, and information of the MME pool, to which the Relay eNB belongs.
Step 310: The DeNB sends the X2 establishment response message to the Relay eNB. The X2 establishment response message includes cell information of the DeNB, and optionally includes the information of neighboring cell of the DeNB and information of the MME pool to which the DeNB belongs.
The Home eNB is a plug and play eNB, including the Home eNB (HeNB) and Home Node B (HNB). The HeNB is used in the LTE and LTE-A systems. The HNB is used in the Universal Mobile Telecommunication System (UMTS) system. The HeNB connects with the HeNB gateway through the S1 interface and the HeNB gateway connects with the MME/S-GW through the S1 interface. In addition, the Home eNB may also directly connect with the MME/S-GW without the GW.
Since in the handover process of the UE, the source eNB and target eNB connect with each other through the X2 interface, the UE may switch from the Relay eNB or the HeNB to other eNBs, or switch from the eNB to the Relay eNB or HeNB, the X2 interface connection needs to be established between the Relay eNB or HeNB and other eNBs in advance. However, the method of the related art only discloses establishing the X2 interface between the Relay eNB and the DeNB, but does not disclose a method for establishing the X2 interface connection between the Relay eNB or HeNB and other eNBs. Thus, X2 interface based applications such as the mobile handover cannot be implemented.